In the market, internal combustion engine are known which are used in motor vehicles. In such a case, the setting of the accelerator is interpreted as the driver's desired torque. This is recalculated to a setpoint air charge in the combustion chamber, from which, in turn, a setpoint throttle valve setting is calculated and is set via a controller. Using an intake-manifold pressure sensor or an air mass flow sensor, an actual air charge in the combustion chamber is determined. From this, in turn, the fuel mass that is to be injected is calculated which, in the last analysis, is set via the duration of the opening of a fuel injector assigned to a combustion chamber in such a way that the stoichiometric ratio of air and fuel (14.7:1) in the combustion chamber is maintained as precisely as possible in order to hold down the emission of pollutants.
However, one problem in this context is that, only when an intake valve in the combustion chamber closes, is it finally certain how much air was aspirated into the combustion chamber, that is, how big the actual air charge actually is. But, at this point in time, the injection must already have ended, because a thorough mixing of the air and fuel mixture, which makes good combustion possible, is above all ensured when the injection takes place early, and is even ended already before the intake valve is opened.
Therefore, at the time of the fuel injection, it is required that the actual air charge, which sets in only at a later time, be predicted. This is done in the known method by using a gradient of the pressure in the intake manifold and a predicted setting of the throttle valve. From this is calculated, in several steps, the pressure in the intake manifold at the time of the closing of the intake valve, and from this, in turn, a predicted air charge is calculated.
It is an object of the present invention to improve the precision in the determination of the predicted air charge (or a corresponding quantity, or rather, one that characterizes this quantity), and if possible, to simplify it, in order to save on computing capacity.